1. Field of the Invention
This invention relates to the highly specialized field of backflow-valve testing, an important activity which is subject to stringent government regulation; and more particularly to an equally specialized testing device for facilitating and improving the reliability of such testing.
2. Prior Art
Backflow valves are extensively used in public-works and industrial facilities to prevent fluids from migrating upstream in event of supply-pressure failure or improper overpressurization of discharge points. Upstream movement of fluids in such instances can contaminate upstream supplies, leading to many different kinds of adverse effects--depending upon the type of facility involved.
Such adverse effects include risks of poisoning (in the case of systems handling water, foods, medicaments, or other fluids for ingestion by people or animals), and explosive or corrosive damage to the facility, with consequent fire and health hazards (in the case of facilities handling highly reactive materials). In addition, such effects nearly always lead to protracted and very expensive operational interruptions, and thereby often to severe consequential damages.
On the other hand, the consequences of adverse test reports, to operators of many facilities, are very expensive. This fact, regrettably, leads to a potential for deception through installation of irregular plumbing arrangements, and even to bribery of testing personnel, as well as other abuses.
Thus backflow testing is subject to error through both inadvertence and various kinds of duplicity. The tests can be difficult, requiring carefully selected and trained testing personnel. Personnel must have great alertness, thorough technical comprehension of facility operation--to properly interpret test results, as well as to detect improper plumbing installations--and a high degree of personal integrity.
It is for these reasons that backflow testing in many industrial and public-works fields is governmentally required, regulated, and in some instances conducted. Unfortunately, the number of valves to be tested is enormous, and the number of such qualified personnel relatively small.
In the present document we shall refer to the "upstream", "inlet" or "source" side of a valve, as distinguished from the "downstream", "outlet" or "discharge" side. This terminology departs from popular nomenclature in the backflow-valve industry, which most often refers to the "high pressure" and "low pressure" sides (or sometimes just the "high" and "low" sides) of the valve, respectively.
The nomenclature used in this document is preferred for present purposes, to facilitate unambiguous discussion of abnormal pressurization conditions--which are in fact the entire focus of backflow valves and their testing. Such abnormal conditions run precisely contrary to the implicit assumption that the source side is at a suitably higher pressure than the discharge side.
In addition, there are various types of backflow valves, some having one or more built-in cutoff valves in series with the valve on each side, or providing special pressure-bleeding ports to atmospheric pressure. Such additional valving, and in some cases the resultant added chambers, are incorporated into backflow valves for various reasons, but particularly for convenience in attaching test equipment, and in isolating the pressure-responsive mechanism of the valve from the actual source and discharge plumbing, for testing.
In systems employing valves that lack such built-in features, equivalent test valving is usually included instead in the system plumbing. Hence for relative simplicity and definiteness throughout the remainder of this document, except where otherwise clear from the context, we shall simply refer to the basic backflow valve itself, and its source and discharge ports--disregarding the possible presence of additional valving and chambers.
In interpretation of this document and particularly the appended claims, it is therefore to be understood that our references to the "source" and "discharge" ports or sides of a valve mean the features of the basic backflow valve itself.
The process of testing a backflow valve, even under the best of conditions, necessarily includes performance of at least four functions, or groups of functions, at the same time. These functions include (1) careful and substantially continuous or simultaneous monitoring of pressures on both the upstream and downstream sides of the valve--and, in one way or another, the difference between those two pressures--while (2) making various plumbing connections temporarily, (3) observing and determining performance of the valve under different pressurization conditions, and (4) making permanent, accurate and clear contemporaneous records of both the pressurization conditions and the observed performance of the valve.
Accordingly, such testing requires at least one pressure-measuring instrument, to permit the pressure monitoring just described as the first of the four enumerated functions. As may be appreciated from the above description of functions which must be performed concurrently, the testing heretofore has also called for great presence of mind.
Prior instruments supplied for use in backflow-valve testing exacerbated this latter requirement. As will be explained, they are somewhat cumbersome to use; and have other drawbacks whose recognition forms part of the present invention and thus will be set forth in a later section of this document.
Early backflow-testing instruments included dual-needle mechanical pressure gauges, for connection between the source and discharge sides of the valve under test. One needle registers gauge pressure at one of the two ports, and the other needle the pressure at the other of the ports (i. e., the source and discharge sides of the valve, respectively), each with a display of 200 pounds per square inch full-scale.
As will be appreciated, these dual-readout mechanical gauges are actually rather ingenious, and represented a significant effort in the direction of making the inspector's work humanly possible. In more recent units of the same type, some additional operational aids have been built in.
All these devices, however, remain difficult to use because in proper testing the operating pressure must usually be controlled to a rather close tolerance--which is hard to read on a scale of 200 pounds per square inch. To directly read differential pressure between the two ports, it was necessary to obtain and attach an entirely separate differential gauge and plumbing--typically displaying on a center-zero scale with full-scale excursions of plus-and-minus 15 pounds per square inch. Worse yet, the differential control pressures must be read to a fraction of one pound per square inch, which is hard to read on a scale of plus-and-minus 15 pounds per square inch.
These rather fussy requirements for watching the pressure values, coupled with the familiar "stiction", hysteresis and orientation sensitivity of mechanical valves, makes backflow-valve testing with a dual-needle gauge very awkward, time-consuming and wearying work. Yet many of these instruments remain in use at the time of this writing.
An improved pressure-monitoring instrument for backflow-valve testing has been available for several years. It was developed by two of the present three coinventors, and is manufactured by Fire & Safety Electronics (doing business as Phase Research) of Santa Ana, California, and sold by Duke Products of Irvine, Calif.
The Duke Products unit has two solid-state pressure sensors, attached to the source and discharge sides of the valve respectively. It provides a digital readout derived from a single analog-to-digital converter that is manually switchable between the source- and discharge-pressure sensors.
The same digital readout is also switchable to display the differential pressure. The operator can select any one of the three readouts by operating the display selector switch.
This digital-readout instrument has met with enormous commercial success. That success is considered a testimonial to the difficulty of taking readings to a fraction of one percent of full-scale on a mechanical gauge. Because electro-mechanical sensors, coupled to a digital display, can measure pressure within a tenth of a pound per square inch, the Duke instrument is actually capable of testing operation of a backflow valve to its manufacturer's specifications.
Nevertheless the present inventors have recognized several ways in which the utility of the digital instrument can be even further refined and improved. The specifics of this recognition, and the ways in which the present inventors have succeeded in accomplishing the refinements and improvements, will be set forth in later sections of this document.